Industrial non-destructive testing instruments are used for various types of applications, such as material flaw detection, corrosion monitoring and thickness measurement. The prior art for such devices typically energizes, acquires and processes sensor signals, and issues resulting alarm signals at a substantially faster rate than the rate at which the data associated with said signals are provided to the display for image update. User observation and interpretation of display images are important aspects of the inspection process; therefore, it can pose a problem when the instrument operator cannot be assured that the displayed image is substantially coincident with the alarm event.
It is important to note that it is not uncommon for NDT/NDI instruments to have a display image update at 60 Hz, a rate at which the differences of consecutive image updates can not be discerned by the human eye. The benefit of the instrument operator being assured that the displayed image is substantially coincident with the alarm event is realized when an indication that an alarm event has occurred is shown on the display, and afterwards the operator carefully positions the sensor at a location on the object under inspection that produces a persistent alarm indication. When the position is located, the display image will represent the alarm condition for consecutive 60 Hz updates, thereby allowing the operator to clearly see the persisting alarm event. Typically, the fields of each display image will be comprised of a waveform, waveform markers, numeric readings, and an alarm occurrence indicator. Any one, or a combination, of fields will blink, or otherwise distinctly change, when a persistent alarm condition begins to occur. Furthermore, the display image field update rate of distinctive changes may in some embodiments change at a rate proportional to the number of alarm events per fixed period of time in order to let the operator know the quality of the current inspection measurement. One of the distinctive changes may be changing to a persistent, non-blinking, indication meaning that the highest degree of persistent alarm events is occurring.
One way to address the display/alarm coincidence problem described above is to reduce the measurement and alarm update rate to be less than or equal to the display image update rate; however, this can only be done at the expense of the real time measurement performance of the inspection process. A high frequency measurement rate, as compared to the display image update rate, provides the advantage of higher efficiency because a sensor can be moved at a higher speed along the surface of the object being inspected, or be moved at the regular, or slower, speed with a higher probability of detecting an alarm condition. In the example of a surface scanned at a rate of 10 cm per second, the sensor would traverse 0.167 cm for each 60 Hz measurement rate; however, if the measurement rate was 300 Hz, the sensor would traverse only 0.033 cm for each measurement rate time interval (MTI)—hence, the 300 Hz MTI provides a five fold improvement on scanning resolution. This is why it is not uncommon for NDT/NDI instruments to allow scans to be carried out with a measurement rate in a range of 300˜10,000 Hz.
Alternatively, one could consider increasing the display image update rate to match the measurement rate; however, this is impractical because it places an onerous and unnecessary burden on the instrument's video processing system due to the increased bandwidth requirements and consequential power increase, and many otherwise suitable display technologies are incapable of such a high image update rate.
As a result, which measurement results can be displayed, what characteristics of the measurement may be selected to display, what results are skipped and how results are used in deducing the display result have become an engineering challenge for some to work on. More importantly, how to display an alarm event at a display rate for a real-time alarm event that occurs at the measurement rate has been a challenge to many in the field.
The deficiency of the prior art is obvious in that it does not discriminate between discrete MTI's when it involves providing display image update information; therefore, the instrument operator cannot be assured that the displayed image is substantially coincident with the alarm event. Consequently, any one of the five MTI's is used to update the display image at a 60 Hz rate without any deliberate correlation with the measurement event that caused an alarm.